A note on the Mumford-Tate Conjecture for CM abelian varieties

The Mumford-Tate conjecture is first proved for CM abelian varieties by H. Pohlmann [Ann. Math., 1968]. In this note we give another proof of this result and extend it to CM motives.Comment: 10 pages, to appear in Taiwanese J. Mat

On reduction of Hilbert-Blumenthal varieties

Let $O_F$ be the ring of integers of a totally real field $F$ of degree $g$. We study the reduction of the moduli space of separably polarized abelian $O_F$-varieties of dimension $g$ modulo $p$ for a fixed prime $p$. The invariants and related conditions for the objects in the moduli space are discussed. We construct a scheme-theoretic stratification by $a$-numbers on the Rapoport locus and study the relation with the slope stratification. In particular, we recover the main results of Goren and Oort [GO, J. Alg. Geom. 2000] on the stratifications when $p$ is unramified in $O_F$. We also prove the strong Grothendieck conjecture for the moduli space in some restricted cases, particularly when $p$ is totally ramified in $O_F$.Comment: A shortened revised versio

Variations of mass formulas for definite division algebras

The aim of this paper is to organize some known mass formulas arising from a definite central division algebra over a global field and to deduce some more new ones.Comment: 17 page

Endomorphism algebras of QM abelian surfaces

We determine endomorphism algebras of abelian surfaces with quaternion multiplication.Comment: 14 pages. Lemma 2.10 correcte

bsuˉdˉbs\bar u\bar d : A Promising Detectable Tetraquark

We propose to investigate a particle with four different flavors, $bs\bar u\bar d$, which is a promising detectable tetraquark state. Its $BK$ threshold, 5773 MeV, is 270 MeV higher than the $B_s\pi$ threshold of $bd\bar u\bar s$ and $bu\bar d\bar s$, leading to a large mass region to be stable. If the lowest-lying \bsud state exists below threshold, it can be definitely observed via the weak decay mode $J/\Psi K^-K^-\pi^+$, with the expectation of hundreds of events in the current LHCb data sample but rejecting backgrounds due to its long lifetime. This can be a benchmark of the existence of $X(5568)$ which is a partner of $bs\bar u\bar d$ under the flavor $SU(3)$ symmetry. If no signal is observed in this mode, it constrain the mass of the ground tetraquark state to be larger than the threshold. In the case above threshold, it can be detected via the strong decay mode $\overline B^0K^-$. The $cs\bar u\bar d$ state has similar features.Comment: 5 pages, 2 figures and 2 table

On the existence of maximal orders

We generalize the existence of maximal orders in a semi-simple algebra for general ground rings. We also improve several statements in Chapter 5 and 6 of Reiner's book concerning separable algebras by removing the separability condition, provided the ground ring is only assumed to be Japanese, a very mild condition. Finally, we show the existence of maximal orders as endomorphism rings of abelian varieties in each isogeny class.Comment: 22 pages. To appear in Int. J. Number Theor